During the combustion of fuels in combustion engines acidic combustion products may find their way into the motor oil and thus give rise to corrosion of the engine. In order to neutralize the acidic combustion products, basic salts comprising polyvalent metal salts of naphthenic acids can be dissolved in the motor oil. The stability of solutions of said basic salts in hydrocarbon lubricating oils has been found to be unsatisfactory, and the stability of these solutions becomes even poorer as they contain larger quantities of the basic salts and as the salts have a higher basicity. It has now been found that the stability above 140.degree. C. of said solutions can be considerably improved by the addition of certain polyesters or polyester salts.
Polyesters have been used in a variety of ways in other organic compositions. British Pat. No. GB 2,006,246 discloses polyesters as dispersion agents for pigments in organic liquids. Polyesters were used as anti-foam and anti-squeal agents in U.S. Pat. Nos. 4,428,850, 3,909,425, and 3,429,820. Polyesters were further used to increase the viscosity and yield of sodium base greases in U.S. Pat. No. 2,969,325, and to harden and stabilize anhydrous calcium fatty acid greases at room temperatures in U.S. Pat. No. 2,877,181. However, none of the before mentioned patents discloses the process of the present invention, whereby polyesters and their salts are used to produce concentrated and dilute hydrocarbon lubricating oil compositions of basic salts that are stabilized above 140.degree. C. by the addition of at least one polyester or polyester salt.